The present invention relates to the removal of a layer of material from semiconductor integrated circuit wafers during the course of circuit fabrication, and relates particularly to stripping of resist coatings.
The manufacture of semiconductor integrated circuits requires a substantial number of process steps including, typically, photoresist stripping carried out at several stages in the fabrication process. Known techniques for stripping such a coating include a dry stripping process in which a gas plasma is brought into contact with the coating and a wet stripping process in which a chemical solution is brought into contact with the coating to effect dissolution of the coating material. These stripping processes are typically associated with subsequent rinsing, cleaning and drying operations. A photoresist stripping procedure may involve all of these individual process steps.
The yield of a complete semiconductor wafer fabrication procedure depends to a large extent on the total number of steps involved since each individual step will produce at least a limited number of rejects. To the extent that individual processes can be integrated into, essentially, a single operation, the total yield of such a fabrication procedure can be improved.
To date, the complete removal of a photoresist coating has required a not insignificant number of individual steps, and since different photoresist coatings must be stripped a number of times from a wafer during a complete fabrication procedure, this operation constitutes a significant source of rejects.
Photoresist stripping operations are complicated by the fact that they must be performed on photoresist coatings having a variety of forms. Thus, during a complete fabrication procedure, it may be necessary to strip heavily implanted photoresist coatings, photoresist coatings which received deep ultraviolet exposures, normal positive and negative photoresists, fluorinated photoresists and plasma hardened photoresists.
According to the practices currently employed in the art, stripping parameters, i.e. process times, chemicals used, etc., are set manually for each type of resist layer to be stripped. Therefore, considerable time is taken for changing these parameters for each different resist layer type.